Messenger RNA (“mRNA”) therapy is becoming an increasingly important approach for the treatment of a variety of diseases. Effective mRNA therapy requires effective delivery of the mRNA to the patient and efficient production of the protein encoded by the mRNA within the patient's body. To optimize mRNA delivery and protein production in vivo, a proper cap are typically required at the 5′ end of the construct, which protects the mRNA from degradation and facilitates successful protein translation. Therefore, the large-scale production of enzymes capable of capping mRNA is particularly important for producing mRNA for therapeutic applications.